# How do sperm find their way? **URL:** \ **Category:** Factual Questions\ **Created:** [May 31, 2005, 10:15pm UTC](https://boards.straightdope.com/t/how-do-sperm-find-their-way/306279 "2005-05-31T22:15:45Z")\ **Posts on this page:** 19\ **Page:** 1
**Author:** ![Pushkin](https://avatars.discourse-cdn.com/v4/letter/p/ee59a6/32.png) [@Pushkin](https://boards.straightdope.com/u/Pushkin)\ **Post date:** [May 31, 2005, 10:15pm UTC](https://boards.straightdope.com/t/how-do-sperm-find-their-way/306279/1 "2005-05-31T22:15:45Z")
Having impregnated my ex-girlfriend about six or seven odd weeks ago, just how did the little guys know where to go? Is it a case of deposting so many of them inside her that the chances were that some were pointing in the right direction and one made it? ---
**Author:** ![Bryan\_Ekers](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bryan_ekers/32/183_2.png) [@Bryan\_Ekers](https://boards.straightdope.com/u/Bryan_Ekers)\ **Post date:** [May 31, 2005, 10:48pm UTC](https://boards.straightdope.com/t/how-do-sperm-find-their-way/306279/2 "2005-05-31T22:48:52Z")
As I understand it, there aren’t a lot of off-ramps. A casual search turns up numerous pages on female anatomy but I’m guessing it’s a matter of unleashing a horde and hoping some can find their way. ---
**Author:** ![Khan](https://avatars.discourse-cdn.com/v4/letter/k/3ab097/32.png) [@Khan](https://boards.straightdope.com/u/Khan)\ **Post date:** [May 31, 2005, 11:06pm UTC](https://boards.straightdope.com/t/how-do-sperm-find-their-way/306279/3 "2005-05-31T23:06:25Z")
It’s been suggested that once the sperm get relatively close to the egg, they’re also guided by a form of chemotaxis, that is, they can detect chemical signals leading to the egg. Temperature may be a factor too, but as I recall from my repro texts that hypothesis is pretty suspicious. There is a measure of randomness involved as you suggested along with a lot of luck (or unluck, depending on how you look at it). Sperm can survive in a woman for several days and could just as well find their way with the benefit of time just as well as they could with numbers. On the other hand, the vagina is pretty acidic compared to what sperm “like” to live in, so that can cut their time short. In addition to that, there’s a mucus barrier at the cervix, if I recall, that can act as a net and trap deformed sperm, or even regular ones that can get tangled up in there. I’ve seen SEM photos of that. It was pretty neat. So it’s a matter of numbers, yes, but also time and possibly other mechanisms such as “sniffing” out the egg with a chemical gradient. ---
**Author:** ![Pedro](https://avatars.discourse-cdn.com/v4/letter/p/919ad9/32.png) [@Pedro](https://boards.straightdope.com/u/Pedro)\ **Post date:** [May 31, 2005, 11:15pm UTC](https://boards.straightdope.com/t/how-do-sperm-find-their-way/306279/4 "2005-05-31T23:15:29Z")
On this subject I’ve always wondered: does sperm know (chemically) which Fallopian tube leads to the egg or does it split randomly between the two tubes, so that approximatelly 50% of the sperm cells choose the one leading to a dead end? ---
**Author:** ![RealityChuck](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/realitychuck/32/195_2.png) [@RealityChuck](https://boards.straightdope.com/u/RealityChuck)\ **Post date:** [May 31, 2005, 11:55pm UTC](https://boards.straightdope.com/t/how-do-sperm-find-their-way/306279/5 "2005-05-31T23:55:07Z")
A lot of the sperm ends up going the wrong way; the system isn’t infallable. Half may indeed go in the wrong direction. However, you only need one. ---
**Author:** ![Anaamika](https://avatars.discourse-cdn.com/v4/letter/a/5f9b8f/32.png) [@Anaamika](https://boards.straightdope.com/u/Anaamika)\ **Post date:** [June 1, 2005, 12:52am UTC](https://boards.straightdope.com/t/how-do-sperm-find-their-way/306279/6 "2005-06-01T00:52:02Z")
> [@Khan](#): > > On the other hand, the vagina is pretty acidic compared to what sperm “like” to live in, so that can cut their time short. In addition to that, there’s a mucus barrier at the cervix, if I recall, that can act as a net and trap deformed sperm, or even regular ones that can get tangled up in there. I’ve seen SEM photos of that. It was pretty neat. And the temperature is too warm inside the human body (why balls hang outside) and there’s bacteria that eat them (the sperm). Really quite inhospitable. ---
**Author:** ![Eleusis](https://avatars.discourse-cdn.com/v4/letter/e/f4b2a3/32.png) [@Eleusis](https://boards.straightdope.com/u/Eleusis)\ **Post date:** [June 1, 2005, 12:53am UTC](https://boards.straightdope.com/t/how-do-sperm-find-their-way/306279/7 "2005-06-01T00:53:54Z")
> [@Khan](#): > > they’re also guided by a form of chemotaxis Wow, who knew the ladies had cabs up in there! How much do you tip a chemotaxi driver? ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [June 1, 2005, 2:11am UTC](https://boards.straightdope.com/t/how-do-sperm-find-their-way/306279/8 "2005-06-01T02:11:53Z")
Mostly it is numbers but they little swimmers can get help. A sexually excited woman can lead to physiological changes in her body that aid the sperm along (muscular contractions of the uterus and fallopian tubes). This is by no means necessary for fertilization to occur but I recall seeing somewhere that a woman who is not stimulated appropriately may actually act to block sperm and she will expel a goodly portion of the semen after copulation. Again, this is by no means a 100% thing either way but her body does what it can one way or another. Once close, as mentioned, the egg sends some chemical signals that help them home in on it. Beyond that it is just numbers. There are approximately 100 million sperm per ejaculation and only about a dozen finish the trip (which can be as fast as 15 minutes or as slow as a few days). ---
**Author:** ![Cartooniverse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cartooniverse/32/3084_2.png) [@Cartooniverse](https://boards.straightdope.com/u/Cartooniverse)\ **Post date:** [June 1, 2005, 2:34am UTC](https://boards.straightdope.com/t/how-do-sperm-find-their-way/306279/9 "2005-06-01T02:34:01Z")
> [@Eleusis](#): > > Wow, who knew the ladies had cabs up in there! How much do you tip a chemotaxi driver? What do you think they do with the foreskins after circumscisions? They tip the chemotaxis. 😃 :eek: ---
**Author:** ![Si\_Amigo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/si_amigo/32/2877_2.png) [@Si\_Amigo](https://boards.straightdope.com/u/Si_Amigo)\ **Post date:** [June 1, 2005, 3:32am UTC](https://boards.straightdope.com/t/how-do-sperm-find-their-way/306279/10 "2005-06-01T03:32:02Z")
Mindless adventurism. Let’s just see where we end up. The hallmark of the male of the species. 😃 ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [June 1, 2005, 4:03am UTC](https://boards.straightdope.com/t/how-do-sperm-find-their-way/306279/11 "2005-06-01T04:03:42Z")
> [@Whack-a-Mole](#): > > A sexually excited woman can lead to physiological changes in her body that aid the sperm along (muscular contractions of the uterus and fallopian tubes). That’s got nothing to do with sexual excitemtnt. Semen contains appreciable amounts of prostaglandins that initiate contraction in smooth muscle. The response is totally involuntary and unconscious and occurs just as readily in cases of rape or artifical insemination as in stimulating sexual encounters. The chemical batteries in sperm wouldn’t last long enough to allow them to actually swim the whole way. This hormone triggered contratcion is also the reason why having sex can actually initiate labour in women and why ejaculation can trigger orgasm in some women. > [@](#): > > This is by no means necessary for fertilization to occur but I recall seeing somewhere that a woman who is not stimulated appropriately may actually act to block sperm and she will expel a goodly portion of the semen after copulation. Most semen will be expelled regardless of stimulation. I’d be very interested in seeing any evidence that degree of stimulation or even awareness of insemination has any effect on fertility. The other major pint that needs to be mentiones is the vaginal mucosa it itself. It naturally forms a fairly stringy mass but during periods of fertility the strings tend to align towards the cervix. That effectively makes millions of little highways for the sperm. It’s very hard to swim across the grain of the strings so the sperm swim along the grain. The mucus ensures that they swim in the right direction rather than randomly stumbling about. ---
**Author:** ![Eleusis](https://avatars.discourse-cdn.com/v4/letter/e/f4b2a3/32.png) [@Eleusis](https://boards.straightdope.com/u/Eleusis)\ **Post date:** [June 1, 2005, 8:36am UTC](https://boards.straightdope.com/t/how-do-sperm-find-their-way/306279/12 "2005-06-01T08:36:01Z")
…taking notes for the wife… > [@Blake](#): > > Semen contains appreciable amounts of prostaglandins that initiate contraction in smooth muscle. It’s good for the heart. Check. Does that include orally ingested semen? 😉 > [@](#): > > …ejaculation can trigger orgasm in some women. Good for stress. Check. 😉 > [@](#): > > The other major pint that needs to be mentiones is the vaginal mucosa A whole PINT! DAMN! OK OK I’M SORRY I’M SORRY :smack: ---
**Author:** ![irishgirl](https://avatars.discourse-cdn.com/v4/letter/i/8edcca/32.png) [@irishgirl](https://boards.straightdope.com/u/irishgirl)\ **Post date:** [June 1, 2005, 11:16am UTC](https://boards.straightdope.com/t/how-do-sperm-find-their-way/306279/13 "2005-06-01T11:16:23Z")
Do you know what constitutes a “normal” sperm count? Ejaculate over 2mls in volume Containing at least 20 million sperm per ml Of which at least 40% of which should be motile And at least 60% of which should look normal. Which means that you can have a lot of funny looking, lazy sperm hanging around as long as you’ve got a good proportion of healthy, moving ones. So while it only takes one sperm, in effect you need to several million decent quality sperm to be in with a chance of having a baby…because yes, they get lost or die before they make it to their final destination. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [June 1, 2005, 11:58am UTC](https://boards.straightdope.com/t/how-do-sperm-find-their-way/306279/14 "2005-06-01T11:58:06Z")
> [@Blake](#): > > Most semen will be expelled regardless of stimulation. I’d be very interested in seeing any evidence that degree of stimulation or even awareness of insemination has any effect on fertility. I recall seeing something awhile back that suggested a woman who is not properly stimulated during intercourse has a less receptive body to allow sperm to reach an egg for fertilization. The reverse is also true…a woman suitably stimulated acts to help sperm reach their destination. This is all relative of course, the help or inhibit are not foolproof either way and the sperm may or may not reach their destination regardless of the woman’s level of excitement. But this being the Straightdope here is a cite but it seems it is a debated question. > [@](#): > > As orgasm becomes imminent, the vagina decreases in size by about 30% and also becomes congested with blood. The uterus then experiences muscular contractions. A woman experiences full orgasm when her uterus, vagina and pelvic muscles undergo a series of rhythmic contractions. > > _\_ > > Debate rages over the “purpose” of female orgasms. Many different theories have been advanced by different scientists, feminists, doctors, and religious groups. > > Some evolutionists believe that female orgasms have a distinct purpose, such as increasing intimacy with a male partner in order to ensure the survival of the pair bond. Others have theorized that they increase fertility by enhancing sperm retention. > > SOURCE: [http://encyclopedia.laborlawtalk.com/Orgasm](http://encyclopedia.laborlawtalk.com/Orgasm) > [@](#): > > Most recently, evolutionary psychologists have been exploring the proposition that female orgasm is a sophisticated adaptation that allows women to manipulate–even without their own awareness–which of their lovers will be allowed to fertilize their eggs. > > _\_ > > Clues for a reasonable adaptation hypothesis were readily available by the late 1960s, when The British Medical Journal published an exchange of letters about the muscular contractions and uterine suction associated with women’s orgasm. In one letter, a doctor reported that a patient’s uterine and vaginal contractions during sex with a sailor had pulled off his condom. Upon inspection, the condom was found in her cervical canal! The doctor concluded that female orgasms pull sperm closer to the egg as well. > > Yet, it was only three years ago that two British biologists, Robin Baker and Mark Bellis, tested the so-called upsuck hypothesis. They were building upon ideas articulated by evolutionary biologist Robert Smith, who suggested that since women don’t have orgasms every time out, female orgasm favors some sperm over others. Baker and Bellis sought to learn just how female orgasms might affect which of a lover’s sperm is used to fertilize a woman’s eggs. > > _\_ > > They discovered that when a woman climaxes any time between a minute before to 45 minutes after her lover ejaculates, she retains significantly more sperm than she does after nonorgasmic sex. When her orgasm precedes her male’s by more than a minute, or when she does not have an orgasm, little sperm is retained. Just as the doctors’ letters suggested decades earlier, the team’s results indicated that muscular contractions associated with orgasm pull sperm from the vagina to the cervix, where it’s in better position to reach an egg. > > SOURCE: [http://cms.psychologytoday.com/articles/pto-19960101-000028.html](http://cms.psychologytoday.com/articles/pto-19960101-000028.html) Hopefully that will do for now. If you want more evidence there is plenty out there. ---
**Author:** ![Billdo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/billdo/32/315_2.png) [@Billdo](https://boards.straightdope.com/u/Billdo)\ **Post date:** [June 1, 2005, 12:21pm UTC](https://boards.straightdope.com/t/how-do-sperm-find-their-way/306279/15 "2005-06-01T12:21:05Z")
> [@Si Amigo](#): > > Mindless adventurism. Let’s just see where we end up. The hallmark of the male of the species. 😃 Actually, I think it’s the refusal to stop and ask for directions. 😉 ---
**Author:** ![Uncommon\_Sense](https://avatars.discourse-cdn.com/v4/letter/u/f9ae1b/32.png) [@Uncommon\_Sense](https://boards.straightdope.com/u/Uncommon_Sense)\ **Post date:** [June 1, 2005, 1:21pm UTC](https://boards.straightdope.com/t/how-do-sperm-find-their-way/306279/16 "2005-06-01T13:21:13Z")
Serious question; Does a longer penis help get the sperm ‘closer’ to it’s final destiny? If so, then why hasn’t the natural course been for man to have a longer penis? ---
**Author:** ![Spiff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/spiff/32/9852_2.png) [@Spiff](https://boards.straightdope.com/u/Spiff)\ **Post date:** [June 1, 2005, 1:41pm UTC](https://boards.straightdope.com/t/how-do-sperm-find-their-way/306279/17 "2005-06-01T13:41:59Z")
> [@Eleusis](#): > > Wow, who knew the ladies had cabs up in there! How much do you tip a chemotaxi driver? Hell, if you can find my keys, we can \*drive \* out! ---
**Author:** ![BobLibDem](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/boblibdem/32/3149_2.png) [@BobLibDem](https://boards.straightdope.com/u/BobLibDem)\ **Post date:** [June 1, 2005, 1:48pm UTC](https://boards.straightdope.com/t/how-do-sperm-find-their-way/306279/18 "2005-06-01T13:48:26Z")
The Y sperms just go madly up the tubes. The X sperms stop for directions. Since there are so many sperm per ejaculation, if they all went blindly then just by sheer chance there would still be hundreds that find their way to the right tube. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [June 1, 2005, 2:02pm UTC](https://boards.straightdope.com/t/how-do-sperm-find-their-way/306279/19 "2005-06-01T14:02:28Z")
> [@Uncommon Sense](#): > > Serious question; > Does a longer penis help get the sperm ‘closer’ to it’s final destiny? > If so, then why hasn’t the natural course been for man to have a longer penis? I doubt it helps much. Ejaculate is forced out of the penis at a pretty good clip so it gets shot up into the woman pretty much as far as it can go before they must swim the rest of the way. I doubt an extra inch or three will make a difference in this. Remember there is a practical limit on how long a human male penis can be before more length becomes more a hindrance than a help. Some men with sufficiently long members can actually bump into the woman’s cervix. I have been told this is uncomfortable for the woman and probably problematical for the man as well.